The subject of the invention more precisely concerns the inspection of such containers to detect the presence of surface defects on the neck ring of said containers, such as a material defect, called line defect corresponding to excess or shortage of material (line over finish), defects called seeds or blisters, or defects corresponding to a chipped ring.
The state of the art proposes various devices for inspecting the quality of container neck rings so as to eliminate those carrying defects which may detract from their appearance or, more seriously, constitute a true hazard for users. For example, a detection device is known through documents EP 0 497 477 or JP 10 062 359, comprising a light source able to provide an incident beam concentrated on the upper surface of the neck ring. A camera is positioned so as to receive the reflected light beams which are transmitted to a processing unit, adapted to re-constitute an image of the ring surface after rotating the object on a lathe. The processing unit analyses variations of the image in time and space to detect the presence of any defects. Said technical solution does not give satisfaction in practice, insofar as the images suffer from extensive stray light due to the different light reflections on the surface of the container. Surface irregularities of the neck ring generate extensive noise and mask minor defects such as line defects.